جستجوی مقالات مرتبط با کلیدواژه « Recruitment » در نشریات گروه « شیلات »

The life history parameters, including age, growth, mortality and recruitment of Yellowfin hind, Cephalopholis hemistiktos were studied in monthly collected samples from January to December 2018. Otolith was used for age determination. Mean size by the end of each year of life was estimated and showed that, the highest annual increment was identified at the end of the first year of life then gradually decreased with increase of fish age. The estimated von Bertalanffy growth parameters were L∞=43.51 cm, K=0.26 per year, t0=-0.74 year. Asymptotic weight W∞ was estimated as 1375.23 g. The length-weight relationship was W=0.0126 L3.0746 with R2=0.94 for both sexes. The instantaneous rates of total mortality and natural mortality were estimated as 0.77 and 0.49 per year, respectively. The gonado-somatic index showed increasing from April to August with a peak in June for both sexes. Size at first capture (Lc)was estimated as 24.30 cm, which was smaller than the mean size at first sexual maturity 25.31 cm. The value of fishing mortality (F=0.28y-1) was slightly higher than the optimum (Fopt=0.25y-1) and smaller than the limit (Flimit=0.33y-1) biological reference point, indicating that species was exploited within sustainable limit. Estimated parameters and the relative yield-per-recruit analysis showed that this species is not over-exploited.

The current study was carried out on Okpara Stream in Northern Benin to evaluate the demographic factors with inferences on fisheries status of five dominant fish species, which were sampled monthly intervals for 18 months. Asymptotic length (L∞) ranged from 36.23 cm ( Brycinus macrolepidotus ) to 18.8 cm ( Hemichromis fasciatus ). Growth rates (K) varied between 1.6 yr-1 and 0.66 yr-1 with growth performance index (Φ’) ranging from 2.4 to 3.1. Theoretical age at length zero (t0) varied -0.95 year for Marcusenius senegalensis to -0.59 year for Shilbe intermedius . Except for B. macolepidotus , total mortalities were higher than 2 year-1 and length at first capture (L50) ranged 7.72-12.09 cm. Marcusenius senegalensis and S. intermed ius showed one annual peak of recruitment, whereas H. fasciatus , Oreochromis niloticus and B. macrolepidotus displayed two peaks. The results indicated that the stocks of these five species were underexploited. However, the low length at first capture (L50) recorded for some species, requires the implementation of early fisheries management scheme to assure a sustainable exploitation of these fishes.

This study estimated the length-weight relationship, sex ratio and population parameters of mantis shrimp, Harpiosquilla harpax from the coastal waters of Pantai Remis, Perak, Malaysia between February 2012 and October 2012. Total length and weight of 804 specimens of H. harpax were measured and the sex ratio was 1: 0.83 (M: F). Males of H. harpax were dominant over the females throughout the study period. The value of relative growth coefficient (b) for H. harpax was 2.698 for males and 2.884 for females. For the length-weight relationship, the species exhibited negative allometric growth for males, females and combined sexes. The L∞ and K of H. harpax was 18.38 cm and 1.10 yr-1 for males; and 21.53 cm and 0.75 yr-1 for females. The growth performance index (φ') was calculated as 2.57 for males and 2.54 for females. Total mortality (Z), natural mortality and fishing mortality was found to be 4.084 yr-1, 2.247 yr-1 and 1.837 yr-1 for males; whereas 3.259 yr-1, 1.674 yr-1, 1.585 yr-1 for females, respectively. The recruitment pattern of the species was continuous throughout the year for males and females. The exploitation level (E) of H. harpax was estimated at 0.449 for males and 0.486 for females. It is revealed that the stock of H. harpax was very close to optimum level of exploitation (E = 0.50) in the coastal waters of Pantai Remis, Perak, Malaysia.